Various embodiments are explained hereinafter on the basis of the example of a projection device which is based on the so-called “flying spot method”. However, it is also applicable to other projection devices. Referring to FIG. 1, in the so-called “flying spot method”, by means of a two-dimensional micromirror 10, the laser beams from three laser devices 12a, 12b, 12c, which emit red, blue and green light respectively, which is added by means of a beam adding device 14, are deflected and projected onto an image plane 16. The image information is generated by intensity modulation of the three laser light sources 12a, 12b, 12c synchronously with the deflection of the mirror 10. One problem in the construction of a system of this type consists in carrying out the mechanical mounting of the lenses required for beam shaping, which are arranged between the laser devices 12a, 12b, 12c and the beam adding device 14 (not illustrated in FIG. 1), exactly in such a way that the laser beams are accurately superimposed at a defined distance.
This procedure results in a high manufacturing time per system, since adjustment is effected “actively” in this case, that is to say that the laser devices 12a, 12b, 12c have to be driven during lens mounting in such a way that the signals of the three laser devices 12a, 12b, 12c on the display surface 16, the so-called spots, are superimposed. The outlay in respect of machinery also causes high costs, since the adjustment accuracy of the machines for lens positioning has to be in the μm range.
There are then two effects which lead to a misalignment of the spot superimposition and cause a reduction of the contrast, which is associated with an impairment of the image quality of the projection device. A first effect is based on temperature fluctuations during operation, as a result of which the optical system can be altered in such a way that exact beam superimposition can no longer be achieved. A second effect additionally occurs over the lifetime of the projection device. Even if the spots are accurately superimposed at the time of manufacture, it cannot be ruled out that a permanent displacement of the laser spots relative to one another gradually occurs as a result of heating and cooling cycles.